1. Field of the Invention
The present invention relates to a loose-leaf binding tool, particularly to a loose-leaf binding tool of such a type that a fingerhold of an operation plate is pulled or pushed to thereby open/close binding rings.
2. Description of the Related Art
Various types have been proposed with regard to a loose-leaf binding tool of such a type that a fingerhold of an operation plate is pulled or pushed to thereby open/close binding rings. The present invention relates to a binding tool in which two rows of binding rings are fixed to a pair of rotatable shafts which are rotatably supported by a fixed substrate along its longitudinal edges.
FIGS. 1(a), (b), (c) show a main part of this type of conventional loose-leaf binding tool.
This binding tool is constituted of three members: an elongated fixed-side substrate 1 on which a plurality of first binding rings 3 are arranged at predetermined intervals; a rotatable shaft 2 on which a plurality of second binding rings 4 engageable with the first binding rings 3 are disposed and which is attached to one side portion of the substrate 1; and an operation plate 5 disposed along the shaft 2 on the bottom surface of the substrate 1 and movable in a longitudinal direction of the substrate 1. The operation plate 5 has a fingerhold 8 on a front end thereof. The fingerhold is operated forwards/backwards to thereby slide the operation plate 5 in the longitudinal direction of the binding tool, and accordingly the shaft 2 is rotated to close the binding rings 4 on a movable side toward the binding rings 3 on the fixed side or detach the rings 4 from the rings 3.
To transform linear movement of the operation plate 5 into a rotary movement of the shaft, a cam mechanism is formed on facing surfaces of the shaft and the operation plate. That is, a cam protrusion 6 protruding toward the operation plate 5 is disposed on the shaft, and a cam groove 7 into which the cam protrusion 6 fits is disposed in the operation plate 5 (conversely, there is also an example in which the cam protrusion is disposed on the operation plate and the cam groove is disposed in the shaft). The cam groove 7 is shaped in such a manner that when the operation plate 5 is pushed in a push-in position, the shaft 2 is rotated via the cam protrusion 6 to engage the second binding rings 4 with the first binding rings 3. When the operation plate 5 is pulsed in a pull-out position, the shaft 2 is rotated in an opposite direction via the cam protrusion 6 to thereby detach the second binding rings 4 from the first binding rings 3.
In this conventional example, since the movement of the operation plate 5 in the longitudinal direction is smoothly transformed into the rotary movement of the shaft 2, there is no substantial resistance in the operation. Opposite end portions of the cam groove extend in the longitudinal direction. Therefore, there is an advantage that the binding rings 4 on the movable side are stably fixed in closed and opened positions, when the cam protrusion 6 fits in the groove.
However, even when a positional relation between the cam protrusion and the cam groove is designed in such a manner that the binding rings disposed in the closed positions are tightly engaged, a portion is generated in which the engagement between the binding rings is not sufficient. A problem occurs that a part of loose-leaf is bitten between the binding rings by its own weight or an external force such as shock, and therefore there has been a demand for a binding tool which does not have such problem. Another problem is that the opening of the rings of the movable side is not sufficient for inserting and removing sheets of loose leafs having holes.